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Fri, 27 Mar 2020 22:37:59 +0000 (UTC) Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Fri, 27 Mar 2020 15:37:44 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Fri, 27 Mar 2020 15:37:57 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Fri, 27 Mar 2020 15:37:57 -0700 Received: from [10.2.58.50] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 27 Mar 2020 22:37:57 +0000 Subject: Re: [Patch v2 2/2] mm/page_alloc.c: define node_order with all zero To: Wei Yang , CC: , , , References: <20200327220121.27823-1-richard.weiyang@gmail.com> <20200327220121.27823-2-richard.weiyang@gmail.com> From: John Hubbard X-Nvconfidentiality: public Message-ID: <4c9d8138-d379-810f-64e7-0d018ed019df@nvidia.com> Date: Fri, 27 Mar 2020 15:37:57 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200327220121.27823-2-richard.weiyang@gmail.com> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL111.nvidia.com (172.20.187.18) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1585348664; bh=wICTeUYozVm+quzs+Nfk2y7usqwVZCyFqx6HcmkaOZ8=; h=X-PGP-Universal:Subject:To:CC:References:From:X-Nvconfidentiality: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=pHcQG+1rpMLT51VYJ5vwHY3KcztuvUeQ+z9YV1441wO/PKOnEAORx/0rFLZIesauj cfCQneKKlOonMfpsrRG8wh8HKxI5oZhhiCrUvpBLJXv1MJV4pdebOf+0cxhiW1aeE+ HFeJzYf2EOz413btNGdoeSqcyPc186ZSPIL28V4TBBr4wTNfBtz5eyGKVUgQNbcK2A jYRuVnmbl26Yili5U6rQjrl769X4MLM0wBa9MCxLeMvaJ22pJrPC94Nb1hK2emlOs9 Eo69UlF+kwWO+dcpBwZZoqsQi6n2zu2Kv8ruhUnbpW0Wr0jwYUNzP/HxXJMfq6dxb6 Ov/10oWXxUU/g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 3/27/20 3:01 PM, Wei Yang wrote: > Since we always clear node_order before getting it, we can leverage > compiler to do this instead of at run time. > > Signed-off-by: Wei Yang > --- > mm/page_alloc.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index dfcf2682ed40..49dd1f25c000 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -5585,7 +5585,7 @@ static void build_thisnode_zonelists(pg_data_t *pgdat) > > static void build_zonelists(pg_data_t *pgdat) > { > - static int node_order[MAX_NUMNODES]; > + static int node_order[MAX_NUMNODES] = {0}; Looks wrong: now the single instance of node_order is initialized just once by the compiler. And that means that only the first caller of this function gets a zeroed node_order array... > int node, load, nr_nodes = 0; > nodemask_t used_mask = NODE_MASK_NONE; > int local_node, prev_node; > @@ -5595,7 +5595,6 @@ static void build_zonelists(pg_data_t *pgdat) > load = nr_online_nodes; > prev_node = local_node; > > - memset(node_order, 0, sizeof(node_order)); ...and all subsequent callers are left with whatever debris is remaining in node_order. So this is not good. The reason that memset() was used here, is that there aren't many other ways to get node_order zeroed, given that it is a statically defined variable. > while ((node = find_next_best_node(local_node, &used_mask)) >= 0) { > /* > * We don't want to pressure a particular node. > thanks, -- John Hubbard NVIDIA